Sunlight against H. pylori

Helicobacter pylori is a microorganism with an extraordinary capacity for adaptation, and that is exactly what makes it so formidable. Able to colonize the highly acidic environment of the gastric mucosa, this bacterium is responsible for a large share of the chronic gastritis, peptic ulcers and other digestive disorders we suffer today. To fight it, standard medical practice turns to combined therapies of antibiotics and gastric acid inhibitors. Clinical research, however, is watching a growing problem: the rise of bacterial resistance. More and more often, conventional treatment regimens fail to eradicate the pathogen.

In the search for alternatives and complementary routes, science has turned its attention to a key physiological mechanism: the effect of sunlight and endogenous vitamin D synthesis on the immune system of the digestive tract.

The dilemma of «indiscriminate fire» and antibiotics

Classic drug therapies against H. pylori are indispensable in many clinical scenarios, but they carry an important biological dilemma. Broad-spectrum antibiotics act without absolute selectivity: they do not only attack the target bacterium, they can also seriously alter the diversity of the beneficial gut microbiota. That alteration —known as dysbiosis— tends to cause digestive side effects that make it harder to stay on treatment.

This is where boosting the innate immune response becomes relevant. If the gastric epithelium’s own defense mechanisms are reinforced, the body deploys a localized response that fights the microorganism without razing the ecosystem of allied bacteria. And the key to this molecular shield lies, to a large extent, in vitamin D3.

Why does the sun matter so much?

Although it is usually classified as a simple vitamin, vitamin D3 acts in the body as a genuine steroid hormone. Its synthesis begins in the skin, where ultraviolet B (UVB) radiation photosynthesizes 7-dehydrocholesterol into vitamin D. After two stages of metabolic activation —first in the liver and then in the kidney cells— the molecule becomes 1,25-dihydroxyvitamin D3, its biologically active form.

Through the bloodstream, this hormonal form travels to different tissues. Although its best-known historical function is to regulate calcium and phosphorus homeostasis, the epithelial cells lining our gastrointestinal tract have specific receptors to capture it and trigger complex biological responses.

The molecular mechanisms

When vitamin D3 reaches the gastric epithelium, it activates two main routes of cellular defense, both remarkable for their biochemical and immunological precision:

1. Making antimicrobial «darts»: the VDR-CAMP axis

On entering the gastric cell, vitamin D3 binds to the vitamin D receptor (VDR). That binding triggers the genetic transcription that produces antimicrobial peptides of the cathelicidin family (CAMP, and in particular the molecule LL-37).

Cathelicidins work as true endogenous antibiotics. Being cationic peptides (carrying a positive electric charge), they are drawn to and interact electrostatically with the cell membrane of H. pylori, which carries a negative charge. Once docked, cathelicidins disrupt and puncture the bacterium’s wall, destroying the pathogen and reducing its capacity to colonize the gastric mucosa.

2. Dismantling the bacterial hideout: the PDIA3 receptor and the autolysosomal route

H. pylori does not only sit on the surface of the stomach; the scientific evidence shows it can also invade the interior of the gastric cells themselves. Once inside, the bacterium alters the calcium levels of the lysosomes (the organelles in charge of cellular digestion), neutralizing their internal acidity to avoid being destroyed and managing to multiply in a latent state.

Vitamin D3 halts this mechanism through a membrane receptor called PDIA3. By binding to that receptor, vitamin D restores the release of calcium into the lysosomes, giving them back the acidic environment they need to work properly. This process of «recycling and degradation» —known as autophagy— lets the cell identify, trap and destroy the invading bacterium.

UVB radiation+Skin

Vitamin D3

1,25-dihydroxyvitamin D3The active form, in the gastric epithelium

VDR-CAMP axisCathelicidin LL-37 punctures the bacterium

PDIA3 receptorThe lysosome regains its acidity and digests it

What does the science say?

The relationship between the levels of this hormone and gastric infection is not confined to in vitro or animal laboratory models. Numerous epidemiological studies and clinical trials show that vitamin D deficiency is significantly associated with a higher rate of H. pylori colonization, more severe mucosal damage and a greater likelihood of failure in standard eradication treatments.

Conversely, patients with adequate serum levels of vitamin D3 show better bacterial eradication rates and a more moderate gastric inflammatory response.

The clue of the seasons and geography

This biological connection has a direct reflection at the population level. Several epidemiological analyses suggest a correlation between the seasons of the year, geographic latitude and the prevalence of gastric disorders. In winter periods, or in regions at high latitudes with scarce UVB radiation, the general drop in plasma vitamin D levels coincides with a rise in H. pylori complications and a lower success rate for prescribed medical treatments, showing how the surrounding environment shapes our digestive immunity.

The bigger picture

Sun exposure does not on its own replace a diagnosis or the medical treatment prescribed by a specialist. Still, the accumulated scientific evidence invites us to rethink how we understand the prevention and management of digestive disorders. Oral vitamin D3 supplementation is increasingly studied and used in clinical practice as an adjuvant to improve the effectiveness of standard antibiotic therapy, yet cutaneous photosynthesis driven by sunlight remains the most efficient and self-regulated physiological route to maintain the homeostasis of this hormone in the body.

Learning to build healthy habits into daily life —such as responsible, deliberate sun exposure— is a preventive-medicine strategy of the first order. In a context where drug resistance forces us to look for sustainable alternatives, understanding these biochemical routes makes the value of caring for our natural rhythms plain. Something as everyday as taking in sunlight does not only strengthen our skeletal system: it switches on an advanced, intelligent molecular defense system that travels straight from the skin to protect the integrity of our gastric mucosa.

References and scientific support

• When the antibiotic stops working: the world map of resistance. Savoldi, A., Carrara, E., Graham, D. Y., Conti, M., & Tacconelli, E. (2018). Prevalence of antibiotic resistance in Helicobacter pylori: a systematic review and meta-analysis in World Health Organization regions. Gastroenterology, 155(5), 1372-1382.e17. View study on PubMed Central
• Eradication lowers microbiota diversity. Chen, B., Li, X. M., Cai, T., & Wang, F. (2022). Short-term and long-term alterations of gastrointestinal microbiota with different H. pylori eradication regimens: a meta-analysis. Frontiers in Cellular and Infection Microbiology, 12, 913384. View study (DOI)
• From skin to hormone: the full route of vitamin D. Holick, M. F. (2007). Vitamin D deficiency. The New England Journal of Medicine, 357(3), 266-281. View study (DOI)
• The cathelicidin gene is a direct target of the vitamin D receptor. Gombart, A. F., Borregaard, N., & Koeffler, H. P. (2005). Human cathelicidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3. The FASEB Journal, 19(9), 1067-1077. View study (DOI)
• The stomach makes its own antibiotic: LL-37 in the gastric epithelium. Hase, K., Murakami, M., Iimura, M., Cole, S. P., Horibe, Y., Ohtake, T., Obonyo, M., Gallo, R. L., Eckmann, L., & Kagnoff, M. F. (2003). Expression of LL-37 by human gastric epithelial cells as a potential host defense mechanism against Helicobacter pylori. Gastroenterology, 125(6), 1613-1625. View study (DOI)
• Without the vitamin D receptor, mice get infected more. Zhou, A., Li, L., Zhao, G., Min, L., Liu, S., Zhu, S., Guo, Q., Liu, C., Zhang, S., & Li, P. (2020). Vitamin D3 inhibits Helicobacter pylori infection by activating the VitD3/VDR-CAMP pathway in mice. Frontiers in Cellular and Infection Microbiology, 10, 566730. View study on PubMed Central
• Oral vitamin D3 lowers gastric colonization through the VDR-CAMP route. Zhang, Y., Wang, C., Zhang, L., Yu, J., Yuan, W., & Li, L. (2022). Vitamin D3 eradicates Helicobacter pylori by inducing VDR-CAMP signaling. Frontiers in Microbiology, 13, 1033201. View study on PubMed Central
• The bacterium also hides inside the cell. Dubois, A., & Borén, T. (2007). Helicobacter pylori is invasive and it may be a facultative intracellular organism. Cellular Microbiology, 9(5), 1108-1116. View study on PubMed Central
• Vitamin D3 gives the lysosome its acidity back and the intracellular bacterium is degraded. Hu, W., Zhang, L., Li, M. X., Shen, J., Liu, X. D., Xiao, Z. G., Wu, D. L., Ho, I. H. T., Wu, J. C. Y., Cheung, C. K. Y., Zhang, Y. C., Lau, A. H. Y., Ashktorab, H., Smoot, D. T., Fang, E. F., Chan, M. T. V., Gin, T., Gong, W., Wu, W. K. K., & Cho, C. H. (2019). Vitamin D3 activates the autolysosomal degradation function against Helicobacter pylori through the PDIA3 receptor in gastric epithelial cells. Autophagy, 15(4), 707-725. View study on PubMed Central
• Vitamin D deficiency is associated with more eradication failures. El Shahawy, M. S., Hemida, M. H., El Metwaly, I., & Shady, Z. M. (2018). The effect of vitamin D deficiency on eradication rates of Helicobacter pylori infection. JGH Open, 2(6), 270-275. View study on PubMed Central
• Low levels, more infection and a poorer response to treatment. Shafrir, A., Shauly-Aharonov, M., Katz, L. H., Paltiel, O., Pickman, Y., & Ackerman, Z. (2021). The association between serum vitamin D levels and Helicobacter pylori presence and eradication. Nutrients, 13(1), 278. View study on PubMed Central
• Ten studies, the same direction. Yang, L., He, X., Li, L., & Lu, C. (2019). Effect of vitamin D on Helicobacter pylori infection and eradication: a meta-analysis. Helicobacter, 24(5), e12655. View study (DOI)
• A clinical review of vitamin D3 as an adjuvant. Ma, P. F., Zhuo, L., Yuan, L. P., & Qi, X. H. (2024). Recent advances in vitamin D3 intervention to eradicate Helicobacter pylori infection. Journal of Multidisciplinary Healthcare, 17, 825-832. View study on PubMed Central
• Vitamin D as a strategy that does not depend on antibiotics. Golpour, A., Bereswill, S., & Heimesaat, M. M. (2019). Antimicrobial and immune-modulatory effects of vitamin D provide promising antibiotics-independent approaches to tackle bacterial infections — lessons learnt from a literature survey. European Journal of Microbiology and Immunology, 9(3), 80-87. View study on PubMed Central
• Peptic ulcer has a season and a geography too. Yaratha, K., Talemal, L., Monahan, B. V., Yu, D., Lu, X., & Poggio, J. L. (2023). Seasonal and geographic variation in peptic ulcer disease and associated complications in the United States of America. Journal of Research in Health Sciences, 23(4), e00595. View study on PubMed Central